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High anxiety lowers the birth rate

By Philip Cohen

San Francisco

FAECES from wild baboons may teach doctors how to treat some forms of
human infertility. After studying hormones in primate droppings, an American
zoologist has concluded that a type of infertility common in humans is a healthy
evolutionary adaptation designed to slow down reproduction in times of stress.
The study suggests that stress reduction could be a powerful therapy for some
infertility problems.

More than 10 per cent of chronic fertility problems in women stem from
inadequate levels of progesterone, the hormone which prepares the lining of the
uterus for pregnancy. When progesterone levels are low, a condition called
luteal-phase deficiency or LPD, the uterus is anaemic and an embryo cannot
successfully implant.

Although some studies have suggested that stress can significantly alter
these hormone levels in humans, the theory has been difficult to prove, because
research usually focuses on women who already have problems with fertility. In
these cases, says Sam Wasser of the University of Washington in Seattle, it is
difficult to separate cause and effect. “Are patients stressed because of their
condition, or do they need treatment because they are stressed out?” he
says.

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To probe this question further, he decided to study a group of animals whose
physiology is extremely similar to humans: the yellow baboons at Mikumi National
Park in Tanzania.

Wasser suspected that stress in the environment plays a major role in the
fertility of healthy baboons. For example, although they mate all year round,
only half as many offspring are conceived during the dry season when food is
scarce and the risk of predation is higher. Most young are conceived in the wet
season, and are weaned the following year in the wet season when they have the
best chance of survival.

Wasser examined hormone levels in the faecal pellets of 30 female baboons
over two years and looked at how these levels related to their fertility. He
reports in the August issue of the journal Biology of Reproduction that
during the stressful dry season, the animals’ bodies adjust so that they need
far more progesterone to sustain a pregnancy. In other words, when conceptions
fail during this season it is because levels of this hormone are too low, a
condition human doctors would call LPD. “What in humans we would call a
deficiency turns out to be one of the most important ways for baboons to time
reproduction,” says Wasser.

He argues that if primate reproductive systems have been tuned by evolution
to react to stresses in the environment, then removing stress might be the best
way to treat some types of infertility.

“It’s a very intriguing result,” says Carolyn Givens, a specialist in
reproductive hormones at the University of California, San Francisco. She
reserves judgment, however, on whether stress reduction could stand on its own
as a treatment for infertility.

Wasser is busy recruiting 1000 infertile couples for a study to test the
theory in humans and investigate how best to incorporate stress reduction into
treatment. “We’d like to know how to identify the patients that will benefit the
most, and how to treat them,” he says.